Auxiliary transmissions having a multi-stage main gearing and a front-mounted group, upstream thereof on the drive train, and a range group, downstream thereof on the drive train, have been known for some time and are preferably used in commercial vehicles. Due to the front-mounted group, usually having a two-stage design and a small transmission ratio increment, also called a splitter group, the transmission ratio increments between the transmission ratio steps of the main gearing are basically halved, resulting in the overall number of available transmission ratio steps being doubled. The use of a normally two-stage range group significantly increases the spread of the overall transmission, and the overall number of available gear ratio steps is again doubled. As a result, in conjunction with a three-stage main gearing (having three forward gears and one reverse gear), a 12-speed auxiliary transmission is obtained (having a total of twelve forward gears and a maximum of four reverse gears), and in conjunction with a four-stage main gearing (having four forward gears and one reverse gear), a 16-speed auxiliary transmission is obtained (having a total of sixteen forward gears and a maximum of four reverse gears).
The auxiliary transmission has significantly more compact dimensions and a lower weight than a single gear box having a comparable number of gears and similar gear stepping and spread. However, as many gear changes in an auxiliary transmission entail changes of transmission ratio steps in several subtransmissions, making them rather complex, most of the known auxiliary transmissions are designed to be shiftable in either a partially automated or fully automated manner.
A process for operating a drive train of a motor vehicle comprising a motor, a multi-group transmission, and a clutch connected between the motor and the multi-group transmission is known for instance from DE102007055720A1. Quick shifting sequences are achieved herein, in that gears are shifted from an actual gear to a target gear without actuating the engaged clutch.